Question

Which of the following statements are correct about $\alpha$-amino acids:

• A. All the amino acids which constitute proteins have D-configuration
• B. Isoelectric point of glycine is $6.1$
• C. Valine is an essential amino acid
• D. In $\alpha$-amino acids the basic group is $(-CO{O}^{\ominus })$ and acidic groups is $(-\stackrel{\oplus }{N}{H}_3)$

Answer 1

Answer: (B), (C), (D)

The correct options are
B Isoelectric point of glycine is $6.1$
C In $\alpha$-amino acids the basic group is $(-CO{O}^{\ominus })$ and acidic groups is $(-\stackrel{\oplus }{N}{H}_3)$
D Valine is an essential amino acid

$pK{a}_1$ and $pK{a}_2$ of Glycine are 2.5 and 9.7 respectively so hence according to the formula $pI=\frac{pK{a}_1+pK{a}_2}{2}$ it comes out the $pI$ for Glycine is 6.1.
Valine is an essential amino acid, hence it must be ingested, usually as a component of proteins. It is synthesized in plants via several steps starting from pyruvic acid.